Magnetoresistance effect device

ABSTRACT

A magnetoresistance effect device having a basic structure wherein a multi-layer film comprising a unit of magnetic layer/non-magnetic layer/magnetic layer/antiferromagnetic layer, or antiferromagnetic layer/magnetic layer/non-magnetic layer/magnetic layer is formed with a protective film on a surface of the magnetoresistance effect device employing one of a metal, oxide material, nitride material, a mixture of oxide and nitride material, a double-layer film of metal/oxide, a double-layer film of metal/nitride, or a double-layer film of metal/(mixture of oxide and nitride) of film thickness between 2 nm and 7 nm.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetoresistance effectdevice for reading an information signal recorded on a magnetic storagemedium using a magnetoresistance effect sensor, and a magnetoresistancedetection system and magnetic storage system.

[0003] 2. Description of the Related Art

[0004] As prior art there is known a magnetoresistance (MR) sensor or amagnetic reading converter called an MR head. This has thecharacteristic feature that it can read data from the surface of amagnetic recording medium with high linear density. An MR sensor detectsa magnetic field signal by means of resistance change as a function ofintensity and direction of magnetic flux sensed by a reading device.Such a prior art MR sensor operates in accordance with the anisotropicmagnetoresistance (AMR) effect whereby one component of the resistanceof the reading device changes in proportion to the square of the cosineof the angle between the magnetisation direction and the direction ofthe sensing current that flows in the device. A more detaileddescription of the AMR effect is given in the article “Memory, Storageand Related Applications” IEEE Trans. on Mag. MAG-11, P. 1039 (1975) byD. A. Thompson et al. (Magnetic recorder for storing magnetic data onthis magnetic storage medium: Thompson). In a magnetic head using theAMR effect, a vertical bias is often applied in order to suppressBarkhausen noise. Antiferromagnetic materials such as FeMn, NiMn ornickel oxide are often used as materials to apply this vertical bias.

[0005] Furthermore, in recent years, a more pronounced magnetoresistanceeffect has been reported in which resistance change of a laminatedmagnetic sensor is caused by spin dependent transfer of conductionelectrons between magnetic layers through a non-magnetic layer and byspin dependent scattering at the layer boundaries association with this.This magnetoresistance effect is called by various names such as the“giant magnetoresistance effect” or “spin valve effect”. Suchmagnetoresistance sensors may be formed of suitable materials and show alarger resistance change with improved sensitivity compared with sensorsin which the AMR effect is employed. In such MR sensors, the in-planeresistance between a pair of ferromagnetic layers separated by anon-magnetic layer changes in proportion to the cosine of the anglebetween the magnetisation directions of the two layers.

[0006] Early Japanese Patent Publication H. 2-61572 discloses alaminated magnetic structure for producing a high MR change generated byantiparallel alignment of magnetisation in magnetic layers. The examplesgiven in this publication of materials that can be used in the laminatedstructure include ferromagnetic transition metals and alloys. Also, aconstruction is disclosed in which an antiferromagnetic layer is addedto one of at least two ferromagnetic layers separated by an intermediatelayer, and it is disclosed that FeMn is suitable as thisantiferromagnetic layer.

[0007] Early Japanese Patent Publication H. 4-358310 discloses an MRsensor independent of direction of current flow through the sensorhaving two thin-film layers of ferromagnetic material partitioned by athin-film layer of non-magnetic metal, wherein the direction ofmagnetisation of the two ferromagnetic thin-film layers are orthogonalin the case where the applied magnetic field is zero and the resistancebetween the two non-coupled ferromagnetic layers changes in proportionto the cosine of the angle between the magnetisation directions of thetwo layers.

[0008] Early Japanese Patent Publication H. 6-203340 discloses an MRsensor based on the above effect including two ferromagnetic thin-filmlayers that are separated by a thin-film layer of non-magnetic metallicmaterial and wherein, when the externally applied magnetic field iszero, the magnetisation of an adjacent antiferromagnetic material layeris maintained perpendicular with respect to the other ferromagneticmaterial layers.

[0009] Early Japanese Patent Publication H. 7-262529 discloses a spinvalve magnetoresistance effect device having a construction: firstmagnetic layer/non-magnetic layer/second magneticlayer/antiferromagnetic layer, using in particular CoZrNb, CoZrMo,FeSiAl, FeSi, or NiFe or material wherein Cr, Mn, Pt, Ni, Cu, Ag, Al,Ti, Fe, Co or Zn is added thereto is employed for the first magneticlayer and the second magnetic layer.

[0010] The invention disclosed in Early Japanese Publication H. 7-202292consists in a plurality of magnetic thin films which are laminated withinterposition of non-magnetic layers onto a substrate and whereinantiferromagnetic thin films are provided adjacently to one softmutually adjacent magnetic thin film with interposition of anon-magnetic thin film. This is a magnetoresistance effect film wherein,if the biasing magnetic field of this antiferromagnetic thin film is Hrand the coercive force of the other soft magnetic thin film is Hc2,Hc2<Hr and wherein the antiferromagnetic material consists of at leastone of NiO, CoO, FeO, Fe2O3, MnO or Cr or a mixture of these.

[0011] Also, the invention disclosed in Japanese Patent Application H.6-214837 and Japanese Patent Application H. 6-269524 consists in amagnetoresistance effect film as described above wherein theantiferromagnetic material is a superlattice selected from at least twoof NiO, NixCo1-xO, and CoO.

[0012] Also, the invention disclosed in Japanese Patent Application H.7-11354 consists in a magnetoresistance effect film as described abovein which the antiferromagnetic material is a superlattice selected fromat least two of NiO, Ni_(x)Co_(1−x)O (x=0.1˜0.9), or CoO and the atomicnumber ratio of Ni to Co in this superlattice is at least 1.0.

[0013] Also, in published Japanese Patent Application H. 7-136670 it isdisclosed that a magnetoresistance effect film as described above is atwo-layer film in which the antiferromagnetic material is obtained bylamination of 10 to 40 Å of CoO onto the antiferromagnetic NiO material.

[0014] However, in the prior art, a magnetoresistance effect devicehaving the basic structure:/magnetic layer/non-magnetic layer/magneticlayer/antiferromagnetic layer/or/antiferromagnetic layer/magneticlayer/non-magnetic layer/magnetic layer is subject to the followingproblems. Specifically, by oxidation of the uppermost layer of thestructure by annealing treatment at 200° C. or more, the exchangecoupling magnetic field Hex or the rate of change of magnetoresistance(MR ratio) is lowered. With a magnetoresistance effect device of thistype, an exchange coupling magnetic field is obtained that is applied tothe fixed magnetic layer from the antiferromagnetic layer, so heattreatment at a temperature of 200° C. or more was often necessary. As aresult, oxidation occurred in this step, which adversely affectedperformance.

[0015] Also, even if an antiferromagnetic material is used of a typewhich does not need heat treatment, at the stage of actuallymanufacturing the read/write head, a step of curing the resist of thewrite head section is indispensable. In this step, heat treatment at atemperature of 200° C. or more was necessary, so oxidation of themagnetoresistance effect film occurred at the stage of processing toform a magnetic head.

[0016] Also, when a metal was employed as the protective film, if thefilm thickness was large, due to the conductivity possessed by themetal, there was the problem that a large sensing current, which did notcontribute to a change in magnetoresistance, flowed in the protectivefilm and as a result the sensor output was lowered. Also, if the filmthickness was small, the oxidation penetrated through the metallic layerinto the magnetoresistance effect section, i.e. it could not serve itsfunction as a protective layer.

SUMMARY OF THE INVENTION

[0017] An object of the present invention is to provide amagnetoresistance effect device and magnetoresistance effect sensor usedby, a magnetoresistance detection system and a magnetic storage systemwhich are of excellent reliability by ensuring prevention of oxidationof the magnetoresistance effect device in the heating step ofmanufacture of the read/write head, a sufficient rate of change ofresistance, a sufficiently large exchange coupling magnetic fieldapplied to the fixed magnetic field layer from the antiferromagneticlayer and a sufficiently small coercive force of the free magnetic layerby providing a suitable protective film on the uppermost layer of themagnetoresistance effect device.

[0018] In order to achieve this object, according to the presentinvention, in a magnetoresistance effect device having a basicconstruction wherein there is formed a unit consisting of multi-layerfilms:/magnetic layer/non-magnetic layer/magneticlayer/antiferromagnetic layer/or/antiferromagnetic layer/magneticlayer/non-magnetic layer/magnetic layer, in a protective film formed onthe magnetoresistance effect device there is employed a film of filmthickness at least 2 [nm] and less than 7 [nm] consisting of a metal,oxide material, nitride material, mixture of oxide material and nitridematerial, metal/oxide double layer film, metal/nitride double layerfilm, or metal/(mixture of oxide and nitride material) double layerfilm.

[0019] If metal is employed as the protective film, the protective filmis electrically conductive, so if the protective film thickness islarge, the proportion of sensing current that is branched into theprotective film is increased. Since the current flowing through theprotective film does not contribute to a change of themagnetoresistance, the rate of change of magnetoresistance of the deviceis decreased, diminishing the output of the head. If the thickness ofthe protective film is small, the current flowing through the protectivefilm is not particularly great, so the decrease in output due tobranching to the protective film is small. On the other hand, if thefilm thickness is small, the effectiveness of the protective film inprotecting the magnetoresistance device from oxidation is decreased.Consequently, there is an optimum region in the film thickness of themetal protective film.

[0020] Oxide or nitride are generally essentially non-conductive, so,even if their film thickness is large, the diminution in the rate ofchange of magnetoresistance due to branching of the sensing current intothe protective film not contributing to change of magnetoresistance,such as happens with a metallic protective film, cannot occur. The filmthickness can therefore be set to a large value, so in thehigh-temperature step in the manufacture of a read/write head, entry ofoxygen into the magnetoresistance effect device can be effectivelyprevented so that finally a large Hex, large MR ratio and small Hc ofthe free magnetic layer can be obtained.

[0021] However, oxide or nitride have poor compatibility at the atomiclevel at the interface with the element constituted by a/magneticlayer/non-magnetic layer/magnetic layer/antiferromagneticlayer/or/antiferromagnetic layer/magnetic layer/non-magneticlayer/magnetic layer unit which may result in slight deterioration ofperformance after the high-temperature process. In this case, betterperformance can be obtained after the high-temperature process byinserting a metal of good compatibility at the atomic level with boththe unit and oxide or nitride between the unit and the oxide or nitride.

[0022] By means of the above, a magnetoresistance effect device and amagnetoresistance effect sensor used in, a magnetoresistance detectionsystem and magnetic storage system can be obtained whereby excellentcharacteristics are obtained in regard to output value, output waveform,and bit error rate and which can provide good characteristics also inregard to thermal reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a diagrammatic view showing the construction of amagnetoresistance effect sensor using a magnetoresistance effect deviceaccording to the present invention;

[0024]FIG. 2 is a diagrammatic view showing the construction of amagnetoresistance effect sensor using a magnetoresistance effect deviceaccording to the present invention;

[0025]FIG. 3(A) is a diagrammatic view showing a read/write head using amagnetoresistance effect device according to the present invention andFIG. 3(B) is a magnetic disk device using this read/write head;

[0026]FIG. 4(A) is a diagram of a magnetic read/write device using amagnetoresistance effect device according to the present invention andFIG. 4(B) is a circuit diagram for detection of the magnetoresistanceeffect;

[0027]FIG. 5 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0028]FIG. 6 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0029]FIG. 7 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0030]FIG. 8 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0031]FIG. 9 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0032]FIG. 10 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0033]FIG. 11 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0034]FIG. 12 is a cross-sectional view showing a magnetoresistanceeffect device according to the present invention;

[0035]FIG. 13 is a table showing the characteristics of a prior artmagnetoresistance effect device in relation to the type of theantiferromagnetic layer;

[0036]FIG. 14 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0037]FIG. 15 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0038]FIG. 16 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0039]FIG. 17 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0040]FIG. 18 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0041]FIG. 19 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0042]FIG. 20 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0043]FIG. 21 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the protective layer;

[0044]FIG. 22 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the type of the antiferromagnetic layer;

[0045]FIG. 23 is a table showing the characteristics of amagnetoresistance effect device according to the present invention inrelation to the structures of FIG. 5 to FIG. 12;

[0046]FIG. 24 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 1 in relation to the type of themagnetoresistance effect device;

[0047]FIG. 25 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 1 in relation to the type of themagnetoresistance effect device;

[0048]FIG. 26 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 1 in relation to the type of themagnetoresistance effect device;

[0049]FIG. 27 is a table showing the correspondence of test manufacturenumber and protective film in FIG. 24 to FIG. 26 and FIG. 28 to FIG. 30;

[0050]FIG. 28 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 2 in relation to the type of themagnetoresistance effect device;

[0051]FIG. 29 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 2 in relation to the type of themagnetoresistance effect device; and

[0052]FIG. 30 is a table showing the characteristics of themagnetoresistance effect sensor of FIG. 2 in relation to the type of themagnetoresistance effect device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] For a shielded type magnetoresistance effect sensor according tothe present invention, the construction shown in FIG. 1 and FIG. 2 maybe employed.

[0054] In the magnetoresistance effect sensor M1 of FIG. 1, a lowershielding layer 2, a lower gap layer 3 and a magnetoresistance effectdevice 6 are laminated onto a substrate 1. A gap-defining insulatinglayer 7 may be laminated on top of these. Lower shielding layer 2 isusually patterned to the appropriate size by a photoresist (PR) step.Magnetoresistance effect device 6 is patterned to the appropriate sizeand shape by a photoresist (PR) step and a vertical bias layer 4 andlower electrode layer 5 are laminated in sequence so as to join at theiredges. Upper gap layer 8 and upper shielding layer 9 are laminated insequence on top of these.

[0055] In the magnetoresistance effect sensor M2 of FIG. 2, a lowershielding layer 12, a lower gap layer 13 and a magnetoresistance effectdevice 16 are laminated onto a substrate 11. Lower shielding layer 12 isusually patterned to the appropriate size by a photoresist (PR) step.Magnetoresistance effect device 16 is patterned to the appropriate sizeand shape by a photoresist (PR) step and a vertical bias layer 14 andlower electrode layer 15 are laminated in sequence thereon so as topartially overlap this. Upper gap layer 18 and upper shielding layer 19are laminated in sequence on top of these.

[0056] As the lower shielding layer of the type of FIG. 1 and FIG. 2,NiFe, CoZr, CoFeB, CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa, CoTaHf,CoNbHf, CoZrNb, CoHfPd, CoTaZrNb, CoZrMoNi alloys, FeAlSi or ironnitride type materials may be employed, their film thickness beingsuitably in the range 0.3˜10 [μm]. Further, as the lower gap layer,alumina, SiO2, aluminium nitride, silicon nitride, or diamond-likecarbon etc. may be employed, a range of use of 0.01˜0.20 [μm] beingpreferred.

[0057] As the lower electrode layer, Zr, Ta, or Mo are desirable eitheralone or as alloys or mixtures thereof. A range of film thickness of0.01˜0.10 [μm] may be employed. As the vertical bias layer, CoCrPt,CoCr, CoPt, CoCrTa, FeMn, NiMn, IrMn, PtPdMn, ReMn, PtMn, CrMn, Nioxide, iron oxide, a mixture of Ni oxide and Co oxide, a mixture of Nioxide and Fe oxide, a Ni oxide/Co oxide double layer film, or a Nioxide/Fe oxide double layer film can be employed.

[0058] As the gap-defining insulating layer, alumina, SiO2, aluminiumnitride, silicon nitride, or diamond-like carbon etc. may be suitablyemployed, preferably being used in a range of 0.005˜0.05 [μm]. As theupper gap layer, alumina, SiO2, aluminium nitride, silicon nitride, ordiamond-like carbon etc. may be suitably employed, preferably being usedin a range of 0.01˜0.20 [μm]. As the upper shielding layer, NiFe, CoZr,or CoFeB, CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa, CoTaHf, CoNbHf,CoZrNb, CoHfPd, CoTaZrNb, CoZrMoNi alloys, FeAlSi or iron nitride typematerials may be employed, their film thickness being suitably in therange 0.3˜10 [μm].

[0059] Such shielded type magnetoresistance effect sensors can form awrite head section with the aid of an inductive coil and can thus beused as a read/write unitary head. FIG. 3 is a diagram of a read/writehead. The read/write head comprises a read head that uses amagnetoresistance effect sensor according to the present invention and awrite head of the inductive type.

[0060] An example is shown in which this is mounted with a write headfor longitudinal magnetic writing, but by combining it with a head forvertical magnetic writing, magnetoresistance effect device 45 accordingto the present invention could be used in vertical writing.

[0061] In a read/write head a read head comprising a lower shield film82, magnetoresistance effect device 45 and electrode 40 and upper shieldfilm 81 and a write head comprising a lower magnetic film 84, coil 41and upper magnetic film 83 are formed on a substrate 50. Upper shieldfilm 81 and lower magnetic film 84 may be common. By means of thisread/write head, signals can be written onto the recording medium andsignals can be read from the recording medium. By thus forming thesensing portion of the read head and the magnetic gap of the write headin overlapping positions on the same slider, positional location ontothe same track can be performed simultaneously. This read/write head isprocessed into a slider and mounted on a magnetic read-write device.

[0062]FIG. 4 is a diagram of a magnetic read/write device using amagnetoresistance effect device according to the present invention. Amagnetoresistance effect device 45 and electrode film 40 are formed on asubstrate 50 that also serves as a head slider 90 and reading isperformed by positional location of this onto magnetic recording medium91. Magnetic recording medium 91 is rotated and head slider 90 is movedrelatively over magnetic recording medium 91 facing it with a height of0.2 [μm] or less or in a contacting condition. By means of thismechanism, magnetoresistance effect device 45 is set in a position inwhich a magnetic signal that is written on magnetic recording medium 91can be read from this leakage magnetic field. For example a fixedcurrent is supplied to magnetoresistance effect device 45 from alow-current power source P and a resistance detector S detects thechange of voltage produced by change of resistance.

[0063]FIG. 5 to FIG. 12 are diagrams of the film structure of amagnetoresistance effect device according to the present invention.

[0064] First of all, the magnetoresistance effect device of FIG. 5 has aconstruction in which an underlayer 101, first free magnetic layer 102,non-magnetic layer 104, MR enhancement layer 105, fixed magnetic layer106, antiferromagnetic layer 107 and protective film 108 aresequentially laminated onto a substrate 100.

[0065] The magnetoresistance effect device of FIG. 6 has a constructionin which an underlayer 101, first free magnetic layer 102, second freemagnetic layer 103, non-magnetic layer 104, MR enhancement layer 105,fixed magnetic layer 106, antiferromagnetic layer 107 and protectivefilm 108 are sequentially laminated onto a substrate 100.

[0066] The magnetoresistance effect device of FIG. 7 has a constructionin which an underlayer 101, first free magnetic layer 102, non-magneticlayer 104, fixed magnetic layer 106, antiferromagnetic layer 107 andprotective film 108 are sequentially laminated onto a substrate 100.

[0067] The magnetoresistance effect device of FIG. 8 has a constructionin which an underlayer 101, first free magnetic layer 102, second freemagnetic layer 103, non-magnetic layer 104, fixed magnetic layer 106,antiferromagnetic layer 107 and protective film 108 are sequentiallylaminated onto a substrate 100.

[0068] The magnetoresistance effect device of FIG. 9 has a constructionin which an underlayer 101, antiferromagnetic layer 107, fixed magneticlayer 106, MR enhancement layer 105, non-magnetic layer 104, first freemagnetic layer 102 and protective film 108 are laminated in sequence onto a substrate 100.

[0069] The magnetoresistance effect device of FIG. 10 has a constructionin which an underlayer 101, antiferromagnetic layer 107, fixed magneticlayer 106, MR enhancement layer 105, non-magnetic layer 104, second freemagnetic layer 103, first free magnetic layer 102 and protective film108 are laminated in sequence on to a substrate 100.

[0070] The magnetoresistance effect device of FIG. 11 has a constructionin which an underlayer 101, antiferromagnetic layer 107, fixed magneticlayer 106, non-magnetic layer 104, first free magnetic layer 102 andprotective film 108 are laminated in sequence on to a substrate 100.

[0071] The magnetoresistance effect device of FIG. 12 has a constructionin which an underlayer 101, antiferromagnetic layer 107, fixed magneticlayer 106, non-magnetic layer 104, second free magnetic layer 103, firstfree magnetic layer 102 and protective film 108 are laminated insequence on to a substrate 100.

[0072] Two or more metals may be employed as underlayer 101.Specifically, a multi-layer film consisting of Ta, Hf, Zr, W, Cr, Ti,Mo, Pt, Ni, Ir, Cu, Ag, Co, Zn, Ru, Rh, Re, Au, Os, Pd, Nb, or V etc.may be employed. For example, a thickness of 0.2˜6.0 [nm] of Ta, 0.2˜1.5[nm] of Hf, or 0.2˜2.5 [nm] of Zr may be employed.

[0073] As the first free magnetic layer 102 and second free magneticlayer 103, NiFe, CoFe, NiFeCo, FeCo, CoFeB, CoZrMo, CoZrNb, CoZr,CoZrTa, CoHf, CoTa, CoTaHf, CoNbHf, CoZrNb, CoHfPd, CoTaZrNb, CoZrMoNialloy or amorphous magnetic material may be employed. As the thicknessof these, 1˜10 [nm] is suitable, and preferably 0.1˜5 [nm].

[0074] As non-magnetic layer 104, Cu, a material obtained by addingabout 1˜20 [at %] of Ag to Cu, a material obtained by adding about 1˜2[at %] of Re to Cu, or a Cu—Au alloy may be employed. A film thicknessof 2˜4 [nm] is preferred.

[0075] As MR enhancement layer 105, Co, NiFeCo, FeCo etc. or CoFeB,CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa, CoTaHf, CoNbHf, CoZrNb,CoHfPd, CoTaZrNb, CoZrMoNi alloy or amorphous magnetic material may beemployed. A film thickness of about 0.5˜5 [nm] is desirable. Although ifan MR enhancement layer 105 is not employed, the MR ratio is loweredcompared with the case where it is employed, the number of manufacturingsteps can be reduced by not employing it.

[0076] As fixed magnetic layer 106, of the group based on Co, Ni, andFe, these may be employed alone, in the form of alloys, or as alaminated film. A film thickness of about 1˜50 [nm] is desirable. Asantiferromagnetic layer 107, FeMn, NiMn, IrMn, PtPdMn, ReMn, PtMn, CrMn,Ni oxide, Fe oxide, a mixture of Ni oxide and Co oxide, a mixture of Nioxide and Fe oxide, a double layer film of Ni oxide/Co oxide, or adouble layer film of Ni oxide/Fe oxide etc. may be employed.

[0077] As protective film 108, metal, oxide, nitride, a mixture of oxideand nitride, a double layer film of metal/oxide, a double layer film ofmetal/nitride, or a double layer film of metal/(mixture of oxide andnitride) may be employed. In the case where a single metallic layer isemployed, this may desirably be one selected from the group of Ti, V,Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os,Ir, Pt and Au, or an alloy of two or more of these. As the oxide ornitride, oxides and nitrides of Si, Al, Ti or Ta are preferred. As themetal in a double-layer film, one or an alloy of two or more selectedfrom the group consisting of Ta, Hf, Zr, W, Cr, Ti, Mo, Pt, Ni, Ir, Cu,Ag, Co, Zn, Ru, Re, Au, Os, Pd, Nb, V or Y may be employed.

[0078] In order to make a comparison with a magnetoresistance effectdevice according to the present invention, using a magnetoresistanceeffect device of the construction of FIG. 5, the characteristics when aprotective film was not employed were examined.

[0079] A Corning 7059 glass substrate of thickness 1.1 [nm] was employedas substrate 100, and Ta of thickness 3.0 [nm] was employed asunderlayer 101. Also, as first free magnetic layer 102, Ni₈₁Fe₁₉ (at %,based on the target composition during deposition by sputtering; whichis not the same as the actual film composition. The same applies to theelements below) of 8.0 [nm] was employed. For the non-magnetic layer104, 2.8 [nm] of Cu were employed. For the MR enhancement layer 105, 4[nm] of Co₉₀Fe₁₀ [at %] were employed. For the fixed magnetic layer 106,2.6 [nm] of Ni₈₁Fe₁₉ [at %] were employed. Also, for the first freemagnetic layer 102, use is made of 8.0 [nm] of Ni₈₁Fe₁₉ (at %, being thetarget composition during film deposition by sputtering; which isdifferent from the film composition. The same applies to the elementslisted below.) For the non-magnetic layer 104, 2.8 [nm] of Cu, for theMR enhancement layer 105, 4 [nm] of Co₉₀Fe₁₀ [at %], for the fixedmagnetic layer 106, 2.6 [nm] of Ni₈₁Fe₁₉ [at %], and for theantiferromagnetic layer 107, 20 [nm] of Fe₅₀Mn₅₀ [at %] were employed.

[0080] When FeMn is employed as antiferromagnetic layer 107, an exchangecoupling magnetic field is applied from antiferromagnetic layer 107 tofixed magnetic layer 106 even without heat treatment, so heat treatmentdoes not need to be performed after film deposition. As a result, a freemagnetic layer coercive force of 1.0 [Oe], an exchange coupling magneticfield Hex of 520 [Oe] applied from the antiferromagnetic layer 107 tothe fixed magnetic layer 106, and an MR ratio of 5.2 [%] were obtained.

[0081] Heat treatment was performed on this magnetoresistance effectdevice at 270° C. for 5 hours. As a result, Hex dropped from 520 [Oe] to220 [Oe] and the MR ratio dropped from 5.2 [%] to 2.8 [%]. The drop inthe MR ratio appears to be associated with changes produced by theannealing processing in the condition of the interface between the Culayer and the magnetic layer, but the drop in Hex is due to oxidation ofthe FeMn layer.

[0082] For substrate 100, a Corning 7059 glass substrate of thickness1.1 [nm] was employed, while for underlayer 101 Ta of 3.0 [nm] and forfirst free magnetic layer 102 Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm] wereemployed. For non-magnetic layer 104, Cu of thickness 2.8 [nm] wasemployed, for MR enhancement layer 109, Co₉₀Fe₁₀ [at %] of thickness 0.4[nm] were employed, for fixed magnetic layer 106, Ni₈₁Fe₁₉ [at %] ofthickness 2.6 [nm], and for antiferromagnetic layer 107, variousmaterials were employed. In order that an exchange coupling force shouldbe applied from antiferromagnetic layer 107 to fixed magnetic layer 106,after film deposition heat treatment was performed under vacuum of3×10⁻⁶ [torr] for 5 hours at the respective temperatures shown in FIG.13.

[0083] The characteristics obtained as a result are shown in FIG. 13.Comparing the characteristics with the characteristics prior to thetreatment in the case where the FeMn described above was employed as theantiferromagnetic layer 107, it can be seen that although the Hc of thefree magnetic layer does not change very much, the MR ratio and the Hexbecome lower. The reason for the low MR ratio is believed to be relatedto the change in the condition of the interface of the Cu layer and themagnetic layer brought about by heat treatment, but the drop in Hex isbelieved to be due to oxidation of antiferromagnetic layer 107.

[0084] Next, the characteristics of a magnetoresistance effect deviceaccording to the present invention will be described.

[0085] In the magnetic resonance effect device of FIG. 5, for substrate100, Corning 7059 glass substrate of thickness 1.1 [nm] was employed;for underlayer 101, Ta of 3.0 [nm] was employed, for first free magneticlayer 102, Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm] was employed, while fornon-magnetic layer 104, Cu of 2.8 [nm], for MR enhancement layer 105,Co₉₀Fe₁₀ [at %] of 0.4 [nm], for fixed magnetic layer 106, Ni₈₁Fe₁₉ [at%] of thickness 2.6 [nm] and for antiferromagnetic layer 107, Ni₄₆Mn₅₄of thickness 20 [nm] were employed, while for protective film 108,various metallic materials of various film thicknesses shown in FIG. 14to FIG. 16 were employed.

[0086] In order for an exchange coupling magnetic field to be appliedfrom antiferromagnetic layer 107 to fixed magnetic layer 106, heattreatment for 5 hours at 270° C. was performed after film deposition,under vacuum of 2×10⁻⁶ [torr]. The characteristics obtained as a resultare shown in FIG. 14 to FIG. 16.

[0087] For each item, the first column indicates the Hc [Oe] of the freemagnetic layer 102, the second column indicates the MR ratio [%], andthe third column indicates the Hex [Oe], respectively. The Hc of thefree magnetic layer 102 is practically fixed for all materials and allfilm thicknesses of protective film 108. The MR ratio decreased withrise in the film thickness of the protective film 108 for all materials.If the film thickness exceeds 7 [nm] the MR ratio in general shows asteep decline. From this, it can be seen that, from the point of view ofthe MR ratio, the film thickness of protective film 108 should suitablybe less than 7 [nm].

[0088] Hex increased monotonically with increase of film thickness ofprotective film 108. Comparatively high values are obtained for filmthicknesses of the protecting film 108 of more than 2 [nm]. From this,it can be seen that, from the point of view of Hex, the film thicknessshould be at least 2 [nm]. It has been found that the range of filmthickness of protective film 108 for which good values are obtained forall of the Hc of the free magnetic layer 102, the MR ratio and Hex isbetween 2 [nm] and 7 [nm].

[0089] In the magnetoresistance effect device of the structure of FIG.5, for substrate 100, Corning 7095 glass substrate of thickness 1.1 [nm]was employed; for underlayer 101, Ta of thickness 1.0 [nm] was employed;for first free magnetic layer 102, Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm]was employed; for non-magnetic layer 104, Cu of thickness 2.8 [nm] wasemployed; for MR enhancement layer 105, Co₉₀Fe₁₀ [at %] of thickness 4.0[nm] was employed; for fixed magnetic layer 106, Ni₈₁Fe₁₉ [at %] ofthickness 2.6 [nm] was employed; for antiferromagnetic layer 107,Ni₄₆Mn₅₄ of thickness 20 [nm] was employed; and for protective film 108,the various materials shown in FIG. 17 were employed (film thickness 50nm).

[0090] In order to enable an exchange coupling between magnetic field tobe applied from antiferromagnetic film 107 to fixed magnetic layer 16,after film deposition, heat treatment was performed for 5 hours at 270°C. under vacuum of 2×10−6 [torr]. The characteristics obtained are shownin FIG. 17.

[0091] In the magnetoresistance effect element of the structure of FIG.5, Corning 7059 glass substrate of thickness 1.1 [nm] was employed forsubstrate 100; Ta of thickness 3.0 [nm] was employed for underlayer 101;Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm] was employed for first freemagnetic layer 102; Cu of thickness 2.0 [nm] was employed fornon-magnetic layer 104; Co₉₀Fe₁₀ [at %] of thickness 0.4 [nm] wasemployed for MR enhancement layer 105; Ni₈₁Fe₁₉ [at %] of thickness 2.6[nm] was employed for fixed magnetic layer 106; and Ni₄₆Mn₅₄ ofthickness 20 [nm] was employed for antiferromagnetic layer 107; while alaminated layer of the metallic protective films (3 [nm]) shown in FIG.18 and an Al oxide protective film (50 [nm]) was employed for protectivefilm 108.

[0092] The metallic protective film was employed in contact with theNiMn layer. In order for an exchange coupling magnetic field to beapplied from antiferromagnetic layer 107 to fixed magnetic layer 106,heat treatment was performed for 5 hours at 270° C. in a vacuum of2×10−6 [torr] after film deposition. The characteristics obtained areshown in FIG. 18. In comparison with the case where an Al oxide layerwas employed on its own, with this protective film, while the freemagnetic layer Hc and MR ratio were practically unchanged, the Hex waslarger for practically all materials.

[0093] In the magnetoresistance effect elements of FIG. 5, for substrate100, there was employed Corning 7059 glass substrate of thickness 1.1[nm]; for underlayer 101 there was employed Ta of thickness 3.0 [nm];for first free magnetic layer 102, there was employed Ni₈₁Fe₁₉ [at %] ofthickness 8.0 [nm]; for non-magnetic layer 104, there was employed Cu ofthickness 3.8 [nm]; for MR enhancement layer 105, there was employedCo₉₀Fe₁₀ [at %] of thickness 0.4 [nm]; for fixed magnetic layer 106,there was employed Ni₈₁Fe₁₉ [at %] of thickness 2.6 [nm]; and forantiferromagnetic layer 107, there was employed Ni₄₆Mn₅₄ of thickness 20[nm]. For protective film 108, a laminated double-layer film consistingof a protective film of Ta (3 [nm]) and the non-metallic protectivefilms shown in FIG. 19 (50 [nm]) was employed.

[0094] The Ta protective film was employed in contact with the NiMnlayer. Heat treatment was performed for 5 hours at 270° C. in a vacuumof 2×10−6 [torr] after film deposition in order to arrange for anexchange coupling magnetic field to be applied from antiferromagneticlayer 107 to fixed magnetic layer 106. The characteristics obtained areshown in FIG. 19.

[0095] For substrate 100, there was employed Corning 7059 glasssubstrate of thickness 1.1 [nm]; for underlayer 101, there was employedTa of thickness 3.0 [nm]; for first free magnetic layer 102, there wasemployed Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm]; for non-magnetic layer104, there was employed Cu of thickness 3.8 [nm]; for MR enhancementlayer 105, there was employed Co₉₀Fe₁₀ [at %] of thickness of 0.4 [nm];for fixed magnetic layer 106 there was employed Ni₈₁Fe₁₉ [at %] ofthickness 2.6 [nm]; and for antiferromagnetic layer 107, there wasemployed Ni₄₆Mn₅₄ of thickness 20 [nm]. A laminated double-layer filmconsisting of a Ta protective film (3 [nm]) and an Al oxide protectivefilm [X nm] was employed for protective film 108.

[0096] The Ta protective film was employed in contact with the NiMnlayer. In order for an exchange coupling magnetic field to be appliedfrom antiferromagnetic layer 107 to fixed magnetic layer 106, heattreatment was performed for 5 hours at 270° C. in a vacuum of 2×10⁻⁶[torr] after film deposition. The characteristics when the thickness ofthe Al oxide layer was varied are shown in FIG. 20. Hc of the freemagnetic layer 102 was practically fixed independent of the filmthickness of the Al oxide layer, but the MR ratio and Hex increased withincrease in film thickness, becoming practically fixed at a filmthickness of above 30 [nm].

[0097] In the magnetoresistance effect sensor of FIG. 5, for substrate100, there was used Corning 7059 glass substrate of thickness 1.1 [nm];for underlayer 101 there was used Ta of thickness 3.0 [nm]; for firstfree magnetic layer 102 there was used Ni₈₁Fe₁₉ [at %] of thickness 8.0[nm]; for non-magnetic layer 104, there was used Cu of thickness 2.8[nm]; for MR enhancement layer 105 there was used Co₉₀Fe₁₀ [at %] ofthickness 0.4 [nm]; for fixed magnetic layer 106, there was usedNi₈₁Fe₁₉ [at %] of 2.6 [nm]; for antiferromagnetic layer 107 there wasused Ni₄₆Mn₅₄ of thickness 20 [nm]; and for protective film 108 therewas employed a laminated double-layer film consisting of a Ta protectivefilm [X nm] and Al oxide protective film (50 [nm]).

[0098] The Ta protective film was employed in contact with the NiMnlayer. In order for an exchange coupling magnetic field to be appliedfrom antiferromagnetic layer 107 to fixed magnetic layer 106, heattreatment was performed for 5 hours at 270° C. in a vacuum of 2×10−6[torr] after film deposition. The characteristics when the Ta layer filmthickness was varied are shown in FIG. 21. Regarding the MR ratio, thiswas practically fixed up to a Ta film thickness of 5.0 [nm], but, above7.0 [nm], tended to decrease. It is believed that this is due to currentbranching into the Ta layer. Hex increased with increase in the Ta layerfilm thickness, reaching a practically constant value at 2.0 [nm] orabove.

[0099] In the magnetoresistance effect elements of FIG. 5, for substrate100 there was employed a Corning 7059 glass substrate of thickness 1.1[nm]; for the underlayer, there was employed Ta of thickness 3.0 [nm];for first free magnetic layer 102 there was employed Ni₈₁Fe₁₉ [at %] ofthickness 8.0 [nm]; for non-magnetic layer 104 Cu of thickness 2.8 [nm]was employed; for MR enhancement layer 105, Co₉₀Fe₁₀ [at %] of 0.4 [nm]thickness was employed; for fixed magnetic layer 106, Ni₈₁Fe₁₉ [at %] of2.6 [nm] was employed; and for antiferromagnetic layer 107, variousmaterials were employed. For protective film 108, there was employed alaminated double-layer film consisting of Ta protective film (3 [nm])and a non-metallic protecting film (50 [nm]). The Ta protective film wasemployed in contact with the NiMn layer etc. (antiferromagnetic layer).

[0100] In order to apply an exchange coupling force from theantiferromagnetic layer to the fixed magnetic layer, heat treatment wasperformed for 5 hours at the temperatures respectively shown in FIG. 22in a vacuum of 3×10−6 [torr] after film deposition. The characteristicsobtained as a result are shown in FIG. 22. In the case of all theantiferromagnetic layers 107, the Hex was found to be improved comparedwith the case where no protective film was employed. Regarding the Hc ofthe free magnetic layer 102 and the MR ratio, in the magnetoresistanceeffect device of the construction of FIG. 5 to FIG. 12, the substrate100, a Corning 7059 glass substrate of thickness of 1.1 [nm] wasemployed; for the underlayer, Ta of thickness 3.0 [nm] was employed; forfirst free magnetic layer 102, Ni₈₁Fe₁₉ [at %] of thickness 8.0 [nm] wasemployed; for second free magnetic layer 103, Co₉₀Fe₁₀ of thickness 1.0[nm] was employed; for non-magnetic layer 103, Cu of thickness 2.8 [nm]was employed; for MR enhancement layer 105, Co₉₀Fe₁₀ [at %] of thickness0.4 [nm] was employed; for fixed magnetic layer 106, Ni₈₁Fe₁₉ [at %] of2.6 [nm] thickness was employed; and for antiferromagnetic layer 107,Ni₄₆Mn₅₄ [at %] of thickness 20 [nm] was employed. For protective film108, a laminated double-layer film consisting of a Ta protective film (3[nm]) and a non-metallic protective film (50 [nm]) was employed.

[0101] The Ta protective film is employed in contact with what is, apartfrom the protective film, the uppermost layer of the magnetoresistanceeffect film (in the construction of FIG. 5˜FIG. 8, this is the NiMnlayer, and, in the construction of FIG. 9˜FIG. 12, this is the NiFelayer). In order for an exchange coupling force to be applied from theantiferromagnetic layer to the fixed magnetic layer, heat treatment wasperformed for 5 hours at 270° C. under vacuum of 3×10⁻⁶ [torr] afterfilm formation. The characteristics obtained as a result are shown inFIG. 23. In the case of all the structures, a satisfactory large Hex isensured.

[0102] Next, examples in which these magnetoresistance effect deviceswere applied to magnetoresistance effect sensors of the shielded typeare illustrated.

[0103] Magnetoresistance effect sensors M1 of FIG. 1 were manufacturedusing magnetoresistance effect devices according to the presentinvention. NiFe was employed as the lower shielding layer 2, whilealumina was employed as the lower gap layer 3. Magnetoresistance effectdevice 6 consists of: Ta (3 [nm])/Ni₈₂Fe₁₈ (7 [nm])/Co₉₀Fe₁₀ [1.0 nm]/Cu[2.5 nm]/Co₉₀Fe₁₀ (1 [nm])/Ni₈₁Fe₁₉ (2.6 [nm])/Ni₄₆Mn₅₄ [20nm]/protective film. These elements were processed to a size of 1×1 [μm]by a PR step. A lower electrode layer 5 of CoCrPt and Mo was laminatedso as to contact the end of this magnetoresistance effect device 6.Alumina was employed as upper gap layer 8, while NiFe was employed asupper shielding layer 9. This magnetoresistance effect sensor M1 wasprocessed to the form of a read/write unitary head as shown in FIG. 3and also processed to the form of a slider. It was then used to recordand reproduce data on a CoCrTa-type magnetic recording medium.

[0104] The write track width was 1.5 [μm], the write gap was 0.2 [μm],the read track width was 1.0 [μm] and the read gap was 0.21 [μm]. Thecoercive force of the magnetic recording medium was 2.5 [kOe]. Thereproduction output was measured for different recording mark lengths.The results of the measurement are shown in FIG. 24 to FIG. 26. Thecorrespondence of sample numbers and protective films in FIG. 24 to FIG.26 is as shown in FIG. 27.

[0105] Next, the magnetoresistance effect sensor M2 of FIG. 2 wasmanufactured using a magnetoresistance effect device according to thepresent invention. For the magnetoresistance effect device 16, thestructure of FIG. 6 was employed, the lower shielding layer 12 beingFeTaN, and the lower gap layer 13 being amorphous carbon. As themagnetoresistance effect device 16, Ta (3 [nm])/Ni₈₂Fe₁₈ (7[nm])/Co₉₀Fe₁₀ [1.0 nm]/Cu [2.5 nm]/Co₉₀Fe₁₀ (1 [nm])/Ni₈₂Fe₁₈ (1[nm])/Ni₄₆Mn₅₄ [20 nm]/protective film was employed, being processed tothe size of 1×1 [μm] by a PR process. A lower electrode layer 15 ofCoCrPt and Mo was deposited so as to partially overlap this magneticeffect resistance device 16. Alumina was employed as upper gap layer 18and NiFe was employed as upper shielding layer 19.

[0106] This magnetoresistance effect sensor M2 was processed to the formof a integral read/write head H and processed to the form of a sliderand used to record and reproduce data on to a magnetic recording mediumof the CoCrTa type. The write track width was 1.5 [μm], the write gapwas 0.2 [μm], the read track width was 1.0 [μm] and the read gap was0.21 [μm]. The coercive force of the magnetic recording medium was 2.5[kOe]. The reproduction output was measured for different recording marklengths. The results of the measurement are shown in FIG. 28 to FIG. 30.The relationship between sample numbers and protective films in FIG. 28to FIG. 30 are the same as in FIG. 27.

[0107] Next, a magnetic disk apparatus D manufactured by applying thepresent invention will be described with reference to FIG. 3(B). Inmagnetic disk apparatus D, three magnetic disks 91 are provided on abase B, and a head drive circuit and signal processing circuit andinput/output interface (none of these are illustrated) are accommodatedon the back face of base B. At the outside, there is connected a 32-bitbus line (not shown). On both faces of magnetic disk 91, six integralread/write heads H (the other five are not shown) are arranged. A rotaryactuator A for driving read/write head H, its drive and controlcircuitry, and a spindle direct-coupled motor M for disk rotation aremounted thereon. The diameter of disk 91 was 46 [mm], a region of thedisk surface of diameter 10 [mm] to 40 [mm] being employed. Anembedded-type servo system was employed, high density being achievablesince a servo surface is not provided. This device can be directlyconnected as the external storage device of a miniature computer (notshown). The input/output interface incorporates a cache memory and thetransfer speed corresponds to a bus line in the range of 5 to 20megabytes per second. A large-capacity magnetic disk apparatus D couldalso be constructed by connecting a plurality of the present devices,with the provision of an external controller.

[0108] According to the present invention, oxidation of themagnetoresistance effect device in the heating step of manufacture ofthe read/write head can be prevented by providing a suitable protectivefilm on the uppermost layer of the magnetoresistance effect device.Consequently, a magnetoresistance effect device, magnetoresistanceeffect sensor, magnetoresistance detection system, and magnetic storagesystem can be obtained which are of excellent reliability, since theyensure a sufficient rate of change of resistance, a sufficiently largeexchange coupling magnetic field applied from the antiferromagneticlayer to the fixed magnetic layer, and a sufficiently small coerciveforce of the free magnetic layer.

[0109] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristic thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

[0110] The entire disclosure of Japanese Patent Application No. 9-123797(Filed on May 14, 1997) including specification, claims, drawings andsummary are incorporated herein by reference in its entirety.

What is claimed:
 1. A magnetoresistance effect device comprising: afirst magnetic layer; a non-magnetic layer mounted on the first magneticlayer; a second magnetic layer mounted on the non-magnetic layer; anantiferromagnetic layer mounted on the second magnetic layer; and aprotective film formed on the antiferromagnetic layer so as to protectthe antiferromagnetic layer, wherein the protective film is a metal filmhaving a film thickness of 2 nm or more but less than 5 nm.
 2. Amagnetoresistance effect device comprising: a first magnetic layer; anon-magnetic layer mounted on the first magnetic layer; a secondmagnetic layer mounted on the non-magnetic layer; an antiferromagneticlayer mounted on the second magnetic layer; and a protective film formedon the antiferromagnetic layer so as to protect the antiferromagneticlayer, wherein the antiferromagnetic layer compsrises at least one ofPtMn, PtPdMn, RhMn or IrMn, or an alloy of these substance, and theprotective film comprises one or an alloy of two or more selected fromthe group consisting of Ag, Au, Co, Cr, Cu, Hf, Ir, Mo, Nb, Ni, Os, Pd,Pt, Re, Rh, Ru, Ta, Tc, Ti, V, W, Y, Zn and Zr.
 3. A magnetoresistanceeffect device comprising: an antiferromagnetic layer; a non-magneticlayer mounted on the antiferromagnetic layer; a second magnetic layermounted on the non-magnetic layer; a first magnetic layer mounted on thesecond magnetic layer; and a protective film formed on the firstmagnetic layer so as to protect the first magnetic layer, wherein theprotective film is a metal film having a film thickness between 2 nm and7 nm.
 4. A magnetoresistance effect device comprising; anantiferromagnetic layer: a non-magnetic layer mounted on theantiferromagnetic layer; a second magnetic layer mounted on thenon-magnetic layer; a first magnetic layer mounted on the secondmagnetic layer; and a protective film formed on the first magnetic layerso as to protect the first magnetic layer, wherein the antiferromagneticlayer comprises at least one of PtMn, PtPdMn, RhMn or IrMn, or an alloyof these substance, and the protective film comprises one or an alloy oftwo or more selected from the group consisting of Ag, Au, Co, Cr, Cu,Hf, Ir, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Ru, Ta, Tc, Ti, V, W, Y, Zn andZr.
 5. The magnetoresistance effect device of claim 1 wherein the secondmagnetic layer includes an MR enhancement layer.
 6. Themagnetoresistance effect device of claim 2 wherein the second magneticlayer includes an MR enhancement layer.
 7. The magnetoresistance effectdevice of claim 3 wherein the second magnetic layer includes an MRenhancement layer.
 8. The magnetoresistance effect device of claim 4wherein the second magnetic layer includes an MR enhancement layer.